Process for preparing enol acetates of alpha-diketones



Patented Oct. 5, 1948 PROCESS FOR PREPARING ENOL ACETATES OF ALPHA-DIKETONES Hugh J. Hagemeyer, 31x, Kingsport, Tenn, as-

signor to Eastman Kodak Company, Rochester, I N. Y., a corporation of New Jersey No Drawing. Application October 24, 1946, Serial No. 705,479

This invention relates to enol acetates prepared from a-diketones and u-ketocarboxylic esters.

The mono enol acetate of biacetyl has been prepared by the interaction of ketene and blacetyl in the presence of sulfuric acid. See

, Spence and Degering, Jour. Am. Chem. Soc. 66,

1624 (1944) and Hurd, ibid. 66, 2013 (1944).

I have now found that isopropenyl acetate acts upon biacetyl, in the presence of an acid, to give not only the mono enol acetate but the di enol acetate as well. I have found that isopropenyl acetate has many advantages over ketene in the wherein R represents a member selected from the group consisting of a hydrogen atom and an alkyl group, and R1 represents an alkyl group, in the presence of at least one acid catalyst. pare enol acetates from oc-kGllDCELIbOXYIlC esters by condensing iscpropenyl acetate with an czketocarboxylic ester selected from those represented by the following general formula:

wherein R2 represents a member selected from the group consisting of a hydrogen atom and an alkyl group and R3 represents an alkyl group.

Typical a-diketones rep-resented by the above I pre-' '7 Claims. (Cl. 260491) ketobutyrate, ethyl l-ketobutyrate, ethyl l-keton-caproate, ethyl l-ketoisocaproate, ethyl l-ketoisovalerate, ethyl 1-keto-n-valerate, isobutyl 1- keto-n-valerate, etc.

Typical acid catalysts are hydrochloric acid, hydrobromic acid, sulfuric acid, sulfamic acid, chlorosulfonic acid, fluorosulfonic acid: methyl and ethylsulfuric acids, N-acetylsulfamic acid,

- N,N-dimethylsulfamic acid, benzenesulfonic acid,

p-toluenesulfonic acid, ortho phosphoric acid, selenic acid, etc. The group of acid catalysts represented by the following general formula are especially efiicacious:

wherein X represents a halogen atom or a group of atoms containing a non-metallic atom selected from the group consisting of a nitrogen atom and an oxygen atom, said group of atoms being linked formula I are: biacetyl (diacetyl) acetylpropionyl, dipropionyl, acetyl-n-butyryl, acetylcaproyl, acetylisocaproyl, acetylisovaleryl, acety1isobutyryl, dipropionyl, di-n-butyryl, diisobutyryl, propionyl-n-butyryl, propionylvaleryl, etc.

Typical oc-kBt-O-CELI'bOXYllC esters represented by the above general formula II are: methyl pyruvate, ethyl pyruvate, n-propyl pyruvate, n-amyl pyruvate, isoamyl pyruvate, benzyl pyruvate, hexadecyl pyruvate, allyl pyruvate, methyl 1- off the acetone.

to the S atom through said non-metallic atom.

Advantageously the acid catalyst is added to the isopropenyl acetate which is then added to the a-diketone or ock8tOC8.IbOXy1iC ester. The mixture is then allowed to stand for severalhours to come to equilibrium. The acetone (which is generated during the condensation) is then distilled olf through a short column. More advantageously the mixture is heated under a still head. When the still head temperature has reached its lowest point under total reflux, the take-off is adjusted so as to maintain this temperature and the acetone which is formed slowly distills off. In some cases the equilibrium is such that the still head temperature does not necessarily reach the boiling point of acetone, and after a period of refluxing the temperature is raised to distill The acetone obtained is a meas ure of the completeness of the condensation, since for each mole of isopropenyl acetate used up in acetylation, one mole of acetone is formed.

It is preferable to keep the still pot temperature The following examples will serve to illus trate further the manner of practicing my invention.

Example 1.-u-Acetylvinylacetate and 2,3-

diacetoxybutadzene-LS 84 g. of biacetyl, 250g. of isopropenyl acetate,

and a mixture of 1 g. of p-to1uenesu1fonic acid and 1 ml. of sulfuric acid, were refluxed with a slow rate of take-off for 24 hours. During this period the acetone which was formed was slowly removed. The catalyst was now neutralized with anhydrous sodium acetate. The neutralized reaction mixture was distilled under reduced pres.- sure, and 32 grams of e-acetylvinylacetate (the mono enol acetate) and 20 grams of 2,3-diacetoxybutadiene-l,3 boiling at 32 C. and 53 C. respectively, at 5 mm. of mercury pressure, were obtained. The a-acetylvinyl'acetate has-the i le lowing formula:

and physical constants: Nn 1.3911;

D22 1.082 he 2,3:di e tqx but n -1 3 as e f in iel mel CH2=CC=.C1

' o G=O :0 CH3 (5H3 and physical constants: N 1.4372;

.1 38 1.076 Example 2.- Me t h yl aracetoxyacrylcte ll OTC-.0113

17 g. of methyl pyruvate and 30 g. of isopropenyl acetate containing 1,2 g, of sulfuric acid were refluxed with a take-on head to remove the acetone. When the theoretical quantity of acetone had distilled ofi, the residue was treated with anhydrous sodium acetate to neutralize the catalyst. The neutralized reaction mixture was distilled under reduced pressure and methyl u-acetoxyacrylate distilled over at 53.4" C. at 5 mm. of Hg pressure. The methyl c-acetoxyacrylate was redistilled at 112 C. at 100 mm. of Hg pressure. N 1.4089;

In the same manner shown in Example 1, acetylpropionyl can be acetylated to give an enol acetate, using 100 g. of acetyl propionyl instead of the diacetyl; dipropionyl can be acetylated using 114 g. of dipropionyl, di-n-butyryl can bev acetylated using 142 g. of di-n-butyryl; diisobutyryl can be acetylated using 142 g. of diisobutyryl, etc. In the same manner shown in E ample 2, thyl py u a e a be ac t l ei e ne 20 g. of ethyl pyruvate instead of methyl pyruvate; n propyl pyruvate can be acetylated using 22 g. of n-propyl pyruvate, neamyl pyruvate can be acetylated using 27 g. of n-amyl pyruvate, methyl l-ketobutyrate can be acetylated using 20 g. of methyl l-ketobutyrate, etc.

The enol acetates obtained in accordance with my invention readily add chlorine and bromine at the carbonrtorcarbon double bonds, and can be employed to prepare dichlorides and dibromides.

The dienol acetate obtained from biacetyl, viz. 2,3 diacetoxybutadiene-L3 is a new composition of matter.

-I:3ik .tones or the above general formula I wh re n R represents a memherselected from the group consisting of a hydrogen atom and an alkyl group containing from 1 to 3 carbon atoms, and R1 represents a member selected from the group consisting of a primary alkyl group containing from 1 to 4 atoms and an isopropyl group are especially useful in practicing my invention. e-Ketocarboxylic esters of the above general formula II wherein R2 represents a member selected from the group consisting of a hydrogen atom and a primary alkyl group containing from 1 to 5 carbon atoms, and R3 represents a primary alkyl group containing from 1 to 5 carbon atoms, are especially useful in practicing my invention.

What I claim as my invention and desire to be secured by Letters Patent of the United States is;

i. A process for preparing enol acetates comprising condensing, in the presence of an acid catalyst, isopropenyl acetate with a compound selected from the group consisting of the a-diketones represented by the following general formula:

wherein R represents a member selected irom the group consisting of a hydrogen atom and an alkyl group containing from 1 to 3 carbon atoms, and R1 represents a member selected from the group consisting of a primary alkyl group con:- taining from 1 to 4 carbon atoms and an isopropyl group.

2. A process for preparing enol' acetates com prising condensing, in the presence of sulfuric acid, isopropenyl acetate with diketones represented by the following general formula:

wherein lit represents a member selected irom the group consisting of a hydrogen atom and an alkyl group containing from 1 to 3 carbon atoms, and R1 represents a member selected from the group consisting of a primary alkyl group containing from 1 to 4 carbon atoms and an isopropyl group.

3. A process for preparing enol acetateszcomprising condensing, in the presence of sulfuric acid, ispropenyl acetate with biacetyl.

4. A process for preparing enol acetates comprising condensing, in the presence of sulfamic acid, isopropenyl acetate with a compound selected from the group consisting of a-diketones represented by the following general formula:

0 ll H BCH:CCR1

wherein R represents a member selected from the group consisting of a hydrogen atom and an alkyl group containing from 1 to 3 carbon atoms, and R1 represents a member selected irom the group consisting of a primary alkyl group containing from 1 to 4 carbon atoms and an isoprop-yl group.

5. A process for preparing enol acetates comprising condensing, in the presence of sul famic acid, ispropenyl acetate with biacetyl.

6. A process for preparing enol acetates comprising condensing, in the presence of chlorosulfonic acid, isopropenyl acetate with a compound selected from the group consisting of a-diketones represented by the following general formula:

5 s 6 wherein R represents a, member selected from the group consisting of a hydrogen atom anii an REFERENCES CITED alkyl group containing from 1 to 3 carbon atoms, The following references are of record in the and R1 represents a member selected from the file of this p t:

group consisting of a primary alkyl group con- UNITED STATES PATENTS taming from 1 to 4-carbon atoms and an isopropyl group Number Name Date 7. A process for preparing enol acetates com- ,342,612 Hansley et a1 Feb. 22, 1944 prising condensing, in the presence of chlorosul- 21355971 Hansley et a1 ug. 15, 1944 fonic acid, ispropeny] acetate with biacetyl. 10 2,407,301 p nc et a1 p 1946 HU HAGEMEYER, JR 2,407,302 Spence et a1 Sept. 10, 1946 

